Catheters and body probes which are introduced into human body cavities must be soft so as not to cause injuries to the patient. For introducing a catheter or a body probe into the body in a controlled manner, e.g., into a blood vessel, the bladder, the stomach or the intestine, a stiffening element must be introduced into the interior of the hose, so that the hose will be sufficiently stiff during the insertion. Such a stiffening element is referred to as a mandrel.
Often it is customary to first introduce the stiffening element into the body and then to slip the hose over it. Thereafter, the thin mandrel, also referred to as a Seldinger wire, is extracted from the hose.
A known mandrel (Zeitschrift Anaesthesist, 29, 498 to 503) comprises a wire core which is surrounded by a helically or spirally wound single outer wire. The wire core forms a safety wire and governs the stiffness of the mandrel, whereas the outer wire is much thinner and very flexible. The turns of the outer wire are also close together, so that the pitch of the outer wire is 1:1, that is, the distance between the center axes of adjacent turn equals the thickness of the outer wire. Thus, the outer wire is almost transverse to the lengthwise direction of the mandrel. When the mandrel is inserted into a narrow hose, relatively great friction results between the numerous turns of the outer wire and the inside wall of the hose.
It is further known how to embed a guide wire either as single wire or as braid into a thick-walled plastic jacket (EP-PS 0,014,424, DE-GM 81 23 912, DE-GM 81 32 829). The plastic jacket has a cylindrical outer surface whereby the outer surface of the mandrel contacts the entire area of the inner wall of a thin hose. This results in a large-area contact between the mandrel and hose, so that it is often difficult to move the mandrel and hose relative to each other because the friction is great. Even when using especially well-sliding materials, such as FEP or PTFE, the adhesion of the two parts is difficult to overcome because of the surface adhesion of the two smooth polymer surfaces and as a result of curves which the hose assumes in the human body. It is, therefore, very difficult to pull the mandrel out of a narrow hose. The poor displaceability of the mandrel in the hose also leads to an increased assembly time in the manufacturer's plant. As a rule, the hoses are delivered with the mandrel inserted.